In a liquid crystal display device which displays images by arraying multiple pixels in a matrix manner, when the number of pixels is large and a duty ratio is low, an active matrix substrate in which a switching element such as a thin film transistor (TFT) is formed so as to correspond to each pixel is often used (for example, see Japanese Unexamined Patent Publication No. 0501569/2000 (Tokuhyo 2000-501569) (Document 1; published on Feb. 8, 2000, corresponding to the pamphlet of International Publication WO 98/12754, corresponding U.S. Pat. No. 6,087,730, corresponding U.S. Pat. No. 6,410,411), Japanese Unexamined Patent Publication No. 332254/2000 (Tokukai 2000-332254) (Document 2; published on Nov. 30, 2000), Japanese Unexamined Patent Publication No. 188183/2003 (Tokukai 2003-188183) (Document 3; published on Jul. 4, 2003, corresponding U.S. Patent Publication No. 2003/0124778, corresponding U.S. Pat. No. 6,900,464), Japanese Unexamined Patent Publication No. 165688/2004 (Tokukai 2004-165688) (Document 4; published on Jun. 10, 2004, corresponding U.S. Patent Publication No. 2001/0019127, corresponding U.S. Pat. No. 6,335,290, corresponding U.S. Pat. No. 6,534,789)).
A signal voltage is supplied to a pixel electrode via a switching element such as a TFT. In order to enhance retention of the signal voltage, an auxiliary capacitor is formed. For example, an auxiliary capacitor bus line is formed so as to be parallel to a gate bus line so that a capacitance is prepared between the pixel electrode and the auxiliary capacitor bus line.
When an off resistance of the switching element such as the TFT is infinite and there is no leakage in the auxiliary capacitor, a signal voltage having been temporarily stored in the auxiliary capacitor is retained until the signal voltage is rewritten. On the other hand, for example, when there is a leakage current in the TFT, the retained signal voltage gradually decreases. When there is a smaller leakage in the TFT, better image quality is realized.